Distance from the house
The further the garage is from the house, the more you'll pay for new electrics, water and drainage.
A genuinely separate space for a garden office, studio or annex, though it needs its own services, drainage and thermal envelope. Read our full cost guide and use the calculator to see what your project would cost.
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Typical all-in prices including labour, materials, insulation, plastering and VAT. Prices vary with garage condition, specification and region.
| Item | Typical Cost | % of Total |
|---|---|---|
| Garage door removal & wall/window | £1,800 | 13% |
| Insulation (full thermal upgrade) | £2,800 | 21% |
| Flooring & damp-proofing | £1,800 | 13% |
| Electrics & new supply run | £2,800 | 21% |
| Heating extension/connection | £1,500 | 11% |
| Plastering | £1,100 | 8% |
| Decoration | £800 | 6% |
| Building Regs / fees | £900 | 7% |
| Subtotal | £13,500 | 100% |
These figures cover the main trade and material costs for a standard detached single garage of around 15-16m² with a basic-to-mid specification. They assume the garage is close to the existing services. They exclude longer utility connections of £1,000-£7,000 depending on the distance from the house, architectural drawings and structural engineer calculations where needed, plus contractor markup and contingency. This is why the full project cost on this page is £16,000-£35,000. An en suite or higher-spec finish will increase the total cost.
The further the garage is from the house, the more you'll pay for new electrics, water and drainage.
A detached garage often needs its own heating system or new pipework from the house.
All exposed walls and the roof need suitable insulation to meet current Part L standards.
Older or flat roofs may need repairs or replacement before the conversion can begin.
A long drainage run can add significantly to the cost if the nearest connection point is far away.
A detached garage used as an independent annexe may need planning permission rather than Permitted Development.
The most expensive garage conversion is a detached garage as the building is completely separate from the actual house. It has no shared walls, no roof and no common services with the house and so there is more work to be done before it turns into a comfortable living space.
In many cases you will have to run electricity, water and drainage from your home and the garage will also need its own heat and extra insulation. These jobs add thousands to the budget but they also make a detached garage the ideal choice if you plan to build a self contained annexe.
This guide shows you how much a detached garage conversion will cost you, what makes it more expensive and where people typically pay more than they expect.
The average price of converting a detached garage is between £16,000 and £35,000. If you're building a self contained annexe with a bathroom and kitchen then the cost can go way beyond that.
A standard detached garage is around 15 to 20 square meters. Conversion costs should fall in the region of £900 to £1,800 per m². You will also need to pay an extra £2,000 to £7,000 to get the garage connected to your home's electricity, water and drainage system. The exact amount will depend on how far your garage is from the house.
Those utility connections are some of the largest costs on a detached garage conversion. They are also one of the easiest things to undervalue.
A detached garage isn't connected to your house so the builders have more work to do before it becomes a room that you can use all year round.
Most detached garage conversions need:
Nothing here suggests that the garage is in bad shape. It's just the extra work needed to convert your of separate building into living space.
The good news is that detached garages are perfect for self-contained annexes. The services connected together means you have already done a lot of the work essential to independent living.
Utility connections have a big effect on the final cost of a detached garage conversion. The further the garage is from the house, the more work is needed to run cables and pipework.
| Distance from house | Typical cost |
|---|---|
| Under 5m | £1,000 - £2,000 |
| 5-15m | £2,000 - £4,000 |
| Over 15m | £4,000 - £7,000 |
These figures include the work needed to run electricity, water and drainage between the house and the garage. If the drainage can't rely on gravity, a pump may also be needed, which increases the cost.
Measure the distance from your garage to the house before you ask for quotes. It's one of the easiest ways to get a better estimate.
If you want to heating system to the garage separately, you should add another £1,500 to £3,500. The cost depends on the type of heating system and the garage's use.
Labour
Around 60 to 70% of the total cost goes on labour. Detached garage conversions take longer because the building needs new services as well as the usual building work.
Structural work
| Item | Cost |
|---|---|
| Garage door removal and wall infill | £1,400 - £2,000 |
| New window and/or door | £1,200 - £1,800 |
| Floor slab upgrade | £1,000 - £1,800 |
| Roof insulation upgrade | £1,000 - £2,000 |
| Full roof replacement (if needed) | £2,500 - £6,000 |
Insulation
All exterior walls of a detached garage should be insulated as well as the roof and floor. The insulation will cost you around £2,000-£5,000 depending on the size and condition of the garage.
Utility connections and heating
Typically, it costs £2,000 to £7,000 to run electricity, water and drainage from the house to the garage. If you need to heat the garage separately, add another £1,500-£3,500.
Electricals & plumbing
The cost of fitting lights and sockets will cost you between £1,200 and £2,000 once new services are connected to your garage. A bathroom will add between £5,500 and £9,000. A kitchen can add £15,000 to £35,000 depending on size and spec.
Building regulations and professional fees
| Item | Cost |
|---|---|
| Building control application | £400 - £1,200 |
| Architectural drawings | £600 - £2,500 |
| Structural engineer | £500 - £1,400 |
| Use | Cost |
|---|---|
| Home office or hobby room | £16,000 - £20,000 |
| Bedroom | £18,000 - £24,000 |
| Bedroom with en suite | £24,000 - £32,000 |
| Self-contained annexe | £30,000 - £45,000+ |
The cheapest option is a home office or hobby room since it does not require plumbing. A bedroom is a little more expensive and an en suite adds plumbing, drainage and ventilation. The self contained annexe is the most expensive as it requires both a kitchen and a bathroom.
A detached garage is the easiest type of garage to turn into an annexe. The building already stands on its own, so it offers more privacy than an attached or integral garage.
Before you start, there are a few things to check.
Planning permission. If you are going to live in the self-contained annexe full time or let it out, you will need planning permission.
Council tax. An annexe will be given a separate council tax band once it is completed. Before you start the work, check this with your local council if this is true in your case.
Building regulations. The annexe must comply with standard building regulations. Fire safety, ventilation and escape routes are given extra attention, as the building will be used as a self-contained living space.
Access. If the garage is close to a neighbouring residence, you may need a party wall agreement or further approval for drainage work.
In most cases the best place for establishing an annexe is a detached garage, as much of the work to create independent living space is already included in the conversion.
| Region | Typical variation |
|---|---|
| London & South East | 15–25% above national average |
| Midlands & East of England | Close to national average |
| North England | 10–15% below national average |
| Scotland & Wales | 5–20% below national average |
A £22,000 detached garage conversion in one part of the UK could be £25,300 to £27,500 in London or the South East. In many parts of the North and also in Scotland and Wales the same project will be cheaper because labour costs are lower.
Because a detached garage conversion is a bigger project, it's worth getting quotes from a few experienced builders before you make a decision.
Following are a few costs that are easy to miss when you are planning a detached garage conversion.
Utility connections. The further your garage is from the house, the more you'll pay to run electricity, water and drainage.
Roof repairs. A detached garage has its own roof. If it needs replacing rather than insulating, your costs can rise quickly.
Heating. Detached garages often need their own heating system. This isn't always included in the first quote.
Pre-conversion survey (£400 to £800). A survey can uncover problems with the roof, walls or foundations before work starts.
Contingency. Put aside 10 to 15% of your budget for unexpected costs. On a £22,000 project, that's £2,200 to £3,300.
Council tax. If you're building a self-contained annexe, it may receive its own council tax band.
Insurance. Tell your insurer once the conversion is complete, especially if someone will be living in the building.
Detached garage conversion vs house extension
It is still cheaper to convert a detached garage than to build an extension to a house because you don't need to start from scratch. The walls, roof and foundations are already there. Even with new services to pay for, it can still be the cheaper way to get extra living space.
Does it add value?
Converting a garage can be a good way to add value to a home. A separate annexe can be particularly appealing to buyers seeking space for family or guests. But before you move forward, think about the effects of losing the garage to parking or storage.
How to Keep Costs Down
Everything UK homeowners ask us about detached garage conversion costs, planning and building work.
In a detached garage there are no shared walls, roof or services with the house so it will require separate electricity, water, drainage and heating run out to it. This usually adds £2,000 to £7,000 to standard build costs, subject to how far away the garage is from your home.
That depends on the distance. It’s usually a trenching and pipework job instead of a fixed fee, so you’re looking at £1,000 to £2,000 for a job within 5m of the house, £2,000 to £4,000 for 5 to 15m and £4,000 to £7,000 for over 15m.
There is usually no existing central heating system to extend into, so an independent heat source is needed, costing between £1,500 and £3,500 depending on whether you go for electric heating, a new radiator circuit or another option.
A self contained annexe with its own kitchen and bathroom will usually cost between £30,000 and £45,000 or more. A detached garage is often the best type of property to convert to a genuine annexe as the separate structure and services come included in the cost.
Sometimes, sometimes not. Insulating an existing roof in good condition will typically cost between £1,000 and £2,000, while a full roof replacement (if the existing one isn’t sound) will cost between £2,500 and £6,000.
Detached garage conversions typically cost £900 to £1,800 per square metre for the build itself, plus a separate £2,000 to £7,000 for utility connections depending on distance from the house.
Once completed a self contained annexe may be eligible for its own council tax band. Definitely worth checking with your local council before you finalise your design, especially if you are thinking of renting it out.
In addition to the quote above, budget for the distance to connect to utilities, a roof condition survey, an independent heat source and a 10 to 15% contingency. Detached projects have more property-specific variables than the other garage types.